1. Field of the Invention
The present invention relates to microwave-attenuating composite materials. The present invention also relates to methods for preparing such microwave-attenuating composite materials. The present invention also relates to intermediates useful for preparing such microwave-attenuating composite materials. The present invention further relates to devices containing such microwave-attenuating composite materials and methods for preparing such devices. The present invention additionally relates to methods for attenuating microwaves. More specifically, the present invention relates to methods for absorbing microwave radiation, for signal attenuation at appropriate wavelengths, and for isolating transmitting antennas and receiver components in radar sets.
2. Discussion of the Background
Electronic devices are becoming increasingly compact and complex. At microwave frequencies, cross-talk and ringing are becoming serious problems that need to be addressed. In particular, devices such as cellular telephones, pagers, and palm- or lap-size computers contain many circuits that require isolation from each other for maximum performance. In addition, military platforms such as ships and aircraft operate a variety of radio and radar systems that may interfere with each other, thus requiring isolation measures. These systems may consist of passive devices, active devices, or mixtures thereof. The number, sophistication, and cost of these systems continue to rise, while the demand for improved performance moves forward at an even a faster pace.
In order to prevent cross-talk, it is necessary to isolate the components of electronic devices. This may be accomplished by placing a material of defined and controllable shape, which absorbs interfering frequencies of radiation, between the components. However, the gap where the isolating material is placed may be small, complex in shape, and hard to reach. In addition, the isolating material is preferably dimensionally stable, compact and lightweight, chemically inert and mechanically robust, and unaffected by its operating environment.
At present, numerous microwave-absorbing composite materials are made from organic matrix resins and carbonyl iron powder. Typically, the carbonyl iron powder has a density near 7.9 g/cm3, and the composite has a density near 5 g/cm3. The high density of the conventional microwave-absorbing materials presents the serious drawback of imparting a dramatic increase in the weight of any device incorporating such a material, which is especially undesirable in portable, or hand-held devices, such as mobile telephones, lap-top computers, or aircraft.
Moreover, conventional microwave-attenuating materials are not as effective as desired. In this regard, it is noted that on a commercial or industrial scale even small improvements in absorbing microwave radiation, signal attenuation, and isolation of signal devices are economically significant.
Therefore, there remains a critical need for microwave-attenuating composite materials, which do not suffer from this drawback. There also remains a need for methods for preparing such microwave-attenuating composite materials and intermediates useful for preparing such microwave-attenuating composite materials. In addition, there remains a need for devices, which contain such a microwave-attenuating composite material, and methods for preparing such devices. There also remains a need for improved methods of attenuating microwaves.